Spindle motor and disk drive apparatus

ABSTRACT

A spindle motor includes a stationary portion and a rotating portion. The stationary portion includes a shaft and the rotating portion includes a sleeve portion, a hub, a magnet, and a cap. The sleeve portion is arranged opposite to the shaft. The hub is made of metal, and includes a top plate portion extending radially outward from the sleeve portion, and an outer tubular portion extending downward from an outer edge of the top plate portion. The magnet is fixed to the outer tubular portion and is arranged opposite to the stator. The cap is made of metal, and includes an annular plate-shaped portion fixed to an upper surface of the top plate portion. The magnet has a coefficient of thermal expansion greater than that of the hub. The cap has a coefficient of thermal expansion greater than that of both the hub and the magnet.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a spindle motor for use in a disk driveapparatus.

2. Description of the Related Art

Spindle motors arranged to rotate disks about central axes thereof aretypically installed in electronic devices, such as hard disk apparatusesand optical disk apparatuses. Such spindle motors include a stationaryportion fixed to a housing of the electronic device, and a rotatingportion arranged to rotate while supporting the disk(s).

Some known motors used in disk drive apparatuses also include a bearingmechanism using fluid dynamic pressure. A spindle motor disclosed inJP-A 2009-136143 includes a fixed shaft, an annular bearing component, arotor component, and an annular cover. The bearing component is arrangedat an upper end portion of the fixed shaft. The bearing component isdefined integrally with the fixed shaft. The rotor component is arrangedoutside the fixed shaft. The annular cover is arranged above the bearingcomponent. A radially outer end portion of the annular cover is adheredto an upper end portion of the rotor component. An outer circumferentialsurface of the bearing component is arranged opposite to an innercircumferential surface of the upper end portion of the rotor component.A seal gap is defined between the outer circumferential surface of thebearing component and the inner circumferential surface of the upper endportion of the rotor component. The seal gap is covered with the annularcover.

As described in JP-A 2009-136143, in some motors, a cap member arrangedto cover a capillary seal gap is arranged in a rotating portion. In sucha motor, the annular cover is arranged to define a labyrinth sealtogether with an end portion of the shaft, and this reduces exchange ofair and accompanying evaporation of a bearing fluid. For example, in asmall-sized and high-performance electronic device, such as a notebookPC in which a disk drive apparatus is installed, a CPU and the likeinside a case thereof generate a large amount of heat. If the heatgenerated in the CPU and the like is transmitted to the rotating portionof the motor, the heat may cause a deformation and a warping of therotating portion. If this happens, the motor is unable to rotate stably.Accordingly, there is a demand for a motor structure with which a motoris unlikely to be deformed even when the motor is exposed to heat from aheat source, such as the CPU.

SUMMARY OF THE INVENTION

A spindle motor according to a preferred embodiment of the presentinvention includes a stationary portion including a stator, and arotating portion rotatably supported by the stationary portion through alubricating oil. The stationary portion includes a shaft arranged alonga central axis extending in a vertical direction. The rotating portionincludes a sleeve portion, a hub, a magnet, and a cap. The sleeveportion includes an inner circumferential surface arranged opposite toan outer circumferential surface of the shaft. The hub is made of metal,and includes a top plate portion extending radially outward from thesleeve portion, and an outer tubular portion extending downward from anouter edge of the top plate portion. The magnet is made of bondedneodymium, is fixed to the outer tubular portion, and is arrangedopposite to the stator with a gap intervening therebetween. The cap ismade of metal, and includes an annular plate-shaped portion fixed to anupper surface of the top plate portion. The magnet has a coefficient ofthermal expansion that is greater than a coefficient of thermalexpansion of the hub. The cap has a coefficient of thermal expansiongreater than both the coefficients of thermal expansion of the hub andthe magnet.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a disk drive apparatusaccording to a preferred embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of a spindle motor accordingto the above preferred embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view illustrating a sleeve portionaccording to the above preferred embodiment of the present invention andits vicinity.

FIG. 4 is a schematic cross-sectional view illustrating a plate portionaccording to the above preferred embodiment of the present invention andits vicinity.

FIG. 5 is a cross-sectional view illustrating an example modification ofthe above preferred embodiment of the present invention.

FIG. 6 is a cross-sectional view illustrating another examplemodification of the above preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

It is assumed herein that a vertical direction is defined as a directionin which a central axis of a motor extends, and that an upper side and alower side along the central axis of the motor are referred to simply asan upper side and a lower side, respectively.

It should be noted, however, that the above definitions of the verticaldirection and the upper and lower sides should not be construed torestrict relative positions or directions of different members orportions when the motor is actually installed in a device. Also notethat directions parallel to or substantially parallel to the centralaxis are referred to by the term “axial direction”, “axial”, or“axially”, that directions perpendicular to or substantiallyperpendicular to the central axis are simply referred to by the term“radial direction”, “radial”, or “radially”, and that a direction alongor substantially along a circular arc centered on the central axis issimply referred to by the term “circumferential direction”,“circumferential”, or “circumferentially”. Further, the term“perpendicular direction” includes both perpendicular and substantiallyperpendicular directions and the term “parallel direction” includes bothparallel and substantially parallel directions.

FIG. 1 is a cross-sectional view illustrating an internal structure of adisk drive apparatus 1 including a spindle motor 12 (hereinafterreferred to simply as the “motor 12”) according to a preferredembodiment of the present invention. The disk drive apparatus 1preferably is a so-called hard disk drive. The disk drive apparatus 1preferably includes, for example, two flat disks 11 on which informationis recorded, the motor 12, an access portion 13, and a housing 14. Themotor 12 is arranged to rotate while holding the disks 11. The accessportion 13 is arranged to perform reading and writing of informationfrom or to the disks 11. The access portion 13 may be arranged toperform at least one of the reading and the writing of information fromor to the disks 11.

As illustrated in FIG. 1, the housing 14 preferably includes acup-shaped or substantially cup-shaped lower housing member 141 and aplate-shaped upper plate member 142. The disks 11, the motor 12, and theaccess portion 13 are accommodated inside the lower housing member 141.The upper plate member 142 is fitted to the lower housing member 141 todefine the housing 14. An interior space of the disk drive apparatus 1is preferably a clean space with no, or only an extremely small amountof, dirt or dust. According to the present preferred embodiment, theinterior space of the disk drive apparatus 1 is preferably filled withair. Note that the interior space of the disk drive apparatus 1 may befilled with a helium gas, a hydrogen gas, a nitrogen gas, etc. Also notethat the interior space of the disk drive apparatus 1 may be filled witha mixture of any of these gases and air, if so desired.

The two disks 11 are preferably fixed to the motor 12 through a clamper15. The clamper 15 is fixed to the motor 12 to support the disks 11. Aspacer (not shown) is arranged between the two disks 11. The disks 11are fixed to the motor 12 through the clamper 15 and the spacer.

Note that the two disks 11 are fixed while being spaced from each otherin a direction along a central axis J1 of the motor 12. The accessportion 13 preferably includes four heads 131, four arms 132, and a headactuator mechanism 133, for example. Each of the heads 131 is arrangedin close proximity to a corresponding one of the disks 11 to perform thereading and the writing of information from or to the disk 11. Note thateach head 131 may be arranged to perform at least one of the reading andthe writing of information. Each arm 132 is arranged to support aseparate one of the heads 131. The head actuator mechanism 133 isarranged to move each arm 132 to move an associated one of the heads 131relative to the corresponding disk 11. The above mechanism enables eachhead 131 to make access to a desired location on the corresponding disk11 with the head 131 being arranged in close proximity to the rotatingdisk 11. Note that the number of disks 11 is not limited to two, and mayalso be one or more than two.

FIG. 2 is a cross-sectional view illustrating the motor 12 according toa preferred embodiment of the present invention.

The motor 12 is preferably an outer-rotor motor. The motor 12 includes astationary portion 2 and a rotating portion 3. The rotating portion 3 ispreferably rotatably supported by the stationary portion 2 through alubricating oil (not shown).

The stationary portion 2 preferably includes a shaft 21, a base portion22, a plate portion 23, a cup portion 24, and a stator 25.

The shaft 21 is columnar or substantially columnar, and is arranged toextend along the central axis J1 extending in the vertical direction.The plate portion 23 is fixed to the shaft 21 in the vicinity of anupper end portion thereof. In addition, the cup portion 24 is arrangedin the vicinity of a lower end portion of the shaft 21. The shaft 21 ispreferably, for example, made of a metal, such as stainless steel,steel, iron, etc.

In addition, the upper end portion of the shaft 21 is fixed to the upperplate member 142 of the disk drive apparatus 1 (see FIG. 1). The lowerend portion of the shaft 21 is fixed to the base portion 22 through thecup portion 24.

The base portion 22 includes a hole portion (not labeled) defined at acenter thereof. The base portion 22 preferably includes a plate portion221 arranged to extend radially, and a cylindrical or substantiallycylindrical holder portion 222 arranged to project upward from an inneredge of the plate portion 221. The base portion 22 is arranged to defineat least a portion of the lower housing member 141. Note that the baseportion 22 and the lower housing member 141 may be defined by a singlecontinuous monolithic member as illustrated in FIG. 1. Also note thatthe base portion 22 and the lower housing member 141 may alternativelybe defined by separate members. The base portion 22 is defined, forexample, by subjecting a metal, such as an aluminum alloy, to casting,press working, or the like.

The plate portion 23 is an annular or substantially annular member fixedto an outer circumferential surface of the shaft 21. The plate portion23 is arranged to surround the shaft 21 above a flat plate portion 241of the cup portion 24. The plate portion 23 is press fitted to the shaft21 in the vicinity of the upper end portion of the shaft 21, and isfixed to the shaft 21 through an adhesive 90. Note, however, that theshaft 21 and the plate portion 23 may alternatively be defined by asingle continuous monolithic member.

The plate portion 23 according to the present preferred embodimentpreferably includes a circular plate portion 231 and an annularprojecting portion 232. The circular plate portion 231 is fixed to theouter circumferential surface of the shaft 21, and is arranged to extendradially outward from the shaft 21. In more detail, the circular plateportion 231 includes a hole or a through hole. According to the presentpreferred embodiment, the circular plate portion 231 includes thethrough hole, and a top portion of the shaft 21 is accommodated andfixed in the through hole. In addition, the circular plate portion 231is arranged to extend radially outward from the top portion of the shaft21. The annular projecting portion 232 is arranged to extend downwardfrom an outer edge of the circular plate portion 231. The annularprojecting portion 232 is cylindrical or substantially cylindrical. Notethat, although the shaft 21 and the circular plate portion 231 aredefined by separate members according to the present preferredembodiment, the circular plate portion 231 and the shaft 21 mayalternatively be defined by a single continuous monolithic member. Theplate portion 23 is arranged to have a cup-shaped or substantiallycup-shaped vertical sectional cross area with the circular plate portion231 and the annular projecting portion 232. The plate portion 23 isdefined, for example, by subjecting a metal including copper as a maincomponent to a cutting process, or by an injection molding process usinga resin.

The cup portion 24 is an annular portion arranged in the vicinity of thelower end portion of the shaft 21. According to the present preferredembodiment, the shaft 21 and the cup portion 24 are preferably definedby a single continuous monolithic member. Note, however, that the shaft21 and the cup portion 24 may alternatively be defined by separatemembers. The cup portion 24 preferably includes the flat plate portion241, which is arranged to extend radially outward from the shaft 21, anda cylindrical portion 242 arranged to extend upward from an outer edgeof the flat plate portion 241. The cup portion 24 is arranged to have acup-shaped or substantially cup-shaped vertical sectional cross areawith the flat plate portion 241 and the cylindrical portion 242. The cupportion 24 is defined, for example, by subjecting a metal includingcopper as a main component to a cutting process, or by an injectionmolding process using a resin.

The stator 25 is fitted to the base portion 22. The stator 25 isarranged to produce a turning force (a torque) centered on the centralaxis J1 between the stator 25 and a magnet 33 arranged around the shaft21. That is, the stator 25 and the magnet 33 together define a drivingmechanism configured to rotate the rotating portion 3 with respect tothe stationary portion 2.

The stator 25 preferably includes a stator core 251 and a plurality ofcoils 252. The stator core 251 includes an annular core back 71 and aplurality of teeth 72. The core back 71 is fixed to an outercircumferential surface of the holder portion 222 of the base portion22. The teeth 72 are arranged to project radially outward from the coreback 71. The stator core 251 is preferably defined, for example, bylaminated steel sheets, that is, electromagnetic steel sheets placed oneupon another in an axial direction. Each coil 252 is defined by aconducting wire wound around a separate one of the teeth 72.

The rotating portion 3 preferably includes a sleeve portion 31, a hub32, the magnet 33, and a cap 34.

The sleeve portion 31 is cylindrical or substantially cylindrical inshape, and includes an inner circumferential surface arranged oppositeto the outer circumferential surface of the shaft 21. In other words,the sleeve portion 31 is arranged to accommodate the shaft 21. Thesleeve portion 31 is arranged to rotate about the central axis J1 aroundthe shaft 21. The sleeve portion 31 includes an annular portion 311, anouter cylindrical portion 312, an inner cylindrical portion 313, and acommunicating hole 314. The annular portion 311 is cylindrical orsubstantially cylindrical in shape. The annular portion 311 includes thecommunicating hole 314, which is arranged to extend in the axialdirection from an upper surface to a lower surface of the annularportion 311 to pass through the annular portion 311. The outercylindrical portion 312 is a cylindrical or substantially cylindricalportion arranged to extend upward from an outer edge of the annularportion 311. Meanwhile, the inner cylindrical portion 313 is acylindrical or substantially cylindrical portion arranged to extendupward from an inner edge of the annular portion 311. An innercircumferential surface of the annular portion 311 and an innercircumferential surface of the inner cylindrical portion 313 togetherdefine a single continuous surface in the inner circumferential surfaceof the sleeve portion 31. The inner circumferential surface of thesleeve portion 31 and the outer circumferential surface of the shaft 21are arranged radially opposite each other with a slight gap interveningtherebetween. Metal, such as a ferromagnetic stainless steel, forexample, is preferably used as a material of the sleeve portion 31.

The hub 32 preferably includes a top plate portion 321, a tubularportion 322, and a flange portion 323. The top plate portion 321 is adisk-shaped or substantially disk-shaped portion arranged to extendradially outward from an upper end of the outer cylindrical portion 312of the sleeve portion 31. The tubular portion 322 is a cylindrical orsubstantially cylindrical portion arranged to extend downward from anouter edge of the top plate portion 321. Meanwhile, the flange portion323 is a projecting portion arranged to extend radially outward from alower end of the tubular portion 322. Metal, such as a ferromagneticstainless steel, for example, is preferably used as a material of thehub 32. Preferably, a ferritic stainless steel is used. In addition, thehub 32 preferably has a coefficient of thermal expansion of about10.0×10⁻⁶/° C., for example.

According to the present preferred embodiment, the sleeve portion 31 andthe hub 32 are preferably defined by a single continuous monolithicmember. Note, however, that the sleeve portion 31 and the hub 32 may bedefined by separate members, if so desired.

The magnet 33 is fixed to an inner circumferential surface of thetubular portion 322 of the hub 32. The magnet 33 is annular in shape,and is centered on the central axis J1. The magnet 33 is arrangedopposite to the stator 25 with a gap intervening therebetween. Accordingto the present preferred embodiment, an inner circumferential surface ofthe magnet 33 is arranged radially opposite an outer circumferentialsurface of each of the teeth 72 of the stator core 251. In addition, theinner circumferential surface of the magnet 33 is a pole surface inwhich north and south poles are alternately arranged. A neodymium bondedmagnet (Nd—Fe—B BOND MAGNET), for example, is preferably used as themagnet 33. In addition, the magnet 33 preferably has a coefficient ofthermal expansion of about 12.4×10⁻⁶/° C., for example.

The cap 34 is an annular member fixed to an upper surface of the topplate portion 321 of the hub 32. The cap 34 is positioned above an uppercapillary seal portion 51, which will be described below. The cap 34 ispreferably obtained, for example, by subjecting a metal to a cuttingprocess. Note, however, that the cap 34 may be obtained by anothermethod, such as press working, for example. Also note that the cap 34may be a resin-molded article, if so desired.

The cap 34 according to the present preferred embodiment preferablyincludes a plate-shaped portion 341 and a projecting portion 342. Theplate-shaped portion 341 is annular or substantially annular, and isarranged to extend radially. The projecting portion 342 is arranged toproject downward from an inner edge of the plate-shaped portion 341. Aninner circumferential surface of the projecting portion 342 is arrangedradially opposite an outer circumferential surface of the plate portion23 with a slight gap intervening therebetween. Note that the cap 34 mayalternatively be made up of only the plate-shaped portion 341 withoutincluding the projecting portion 342.

A first adhesion region 901 and a second adhesion region 902 over whichthe adhesive 90 is arranged are preferably defined between theplate-shaped portion 341 and the top plate portion 321, as shown in FIG.4. The first adhesion region 901 is arranged between a lower surface ofthe plate-shaped portion 341 and the upper surface of the top plateportion 321. An inside liquid surface 91 of the adhesive 90 is definedat a radially inner end of the first adhesion region 901. According tothe present preferred embodiment, the inside liquid surface 91 ispreferably arranged above an upper surface of the outer cylindricalportion 312. Note, however, that the inside liquid surface 91 may bearranged not above the upper surface of the outer cylindrical portion312 but above the upper surface of the top plate portion 321.

The second adhesion region 902, which includes an outside liquid surface92 of the adhesive 90, is preferably defined radially outside the firstadhesion region 901. The second adhesion region 902 is arranged betweenan outer circumferential surface of the plate-shaped portion 341 and anouter decreased thickness portion 3214, which will be described below.The outer circumferential surface of the plate-shaped portion 341 isopposed to an inner circumferential surface of the outer decreasedthickness portion 3214 with the second adhesion region 902 interveningtherebetween.

Metal, such as a ferromagnetic stainless steel, for example, ispreferably used as a material of the cap 34. Preferably, an austeniticstainless steel is used. In addition, the cap 34 preferably has acoefficient of thermal expansion of about 17.3×10⁻⁶/° C., for example.

FIG. 3 is a schematic cross-sectional view illustrating the sleeveportion 31 and its vicinity. As illustrated in FIG. 3, the lubricatingoil 40 is arranged in a minute gap between the sleeve portion 31 and acombination of the shaft 21, the plate portion 23, and the cup portion24. Examples of the lubricating oil 40 include, for example, apolyolester oil, a diester oil, and other types of oil having ester asits main ingredient.

The upper capillary seal portion 51 is defined by an outercircumferential surface of the annular projecting portion 232 and aninner circumferential surface of the outer cylindrical portion 312 ofthe sleeve portion 31. That is, the outer circumferential surface of theannular projecting portion 232 is preferably arranged radially oppositethe inner circumferential surface of the outer cylindrical portion 312with the upper capillary seal portion 51 intervening therebetween. Inaddition, the upper capillary seal portion 51 is arranged to decrease inradial width with decreasing height.

A lower capillary seal portion 52 is defined by an outer circumferentialsurface of the annular portion 311 and an inner circumferential surfaceof the cylindrical portion 242. That is, the outer circumferentialsurface of the annular portion 311 is arranged opposite to the innercircumferential surface of the cylindrical portion 242 with the lowercapillary seal portion 52 intervening therebetween. In addition, thelower capillary seal portion 52 is arranged to decrease in radial widthwith decreasing height.

A lower surface of the annular projecting portion 232 is arrangedaxially opposite the upper surface of the annular portion 311 with afirst gap 53 intervening therebetween. An upper thrust dynamic pressuregroove array (not shown) is defined in the lower surface of the annularprojecting portion 232 or the upper surface of the annular portion 311inside the first gap 53. The upper thrust dynamic pressure groove arrayis preferably, for example, a groove array arranged in a spiral patternor a groove array arranged in a herringbone pattern. While the motor 12is running, the upper thrust dynamic pressure groove array induces adynamic pressure in the lubricating oil 40, so that an upper thrustdynamic pressure bearing portion is defined in the first gap 53.

An upper surface of the flat plate portion 241 is arranged axiallyopposite the lower surface of the annular portion 311 with a third gap55 intervening therebetween. A lower thrust dynamic pressure groovearray (not shown) is preferably defined in the upper surface of the flatplate portion 241 or the lower surface of the annular portion 311radially inside the communicating hole 314. The lower thrust dynamicpressure groove array is preferably, for example, a groove arrayarranged in a spiral pattern or a groove array arranged in a herringbonepattern. While the motor 12 is running, the lower thrust dynamicpressure groove array induces a dynamic pressure in the lubricating oil40, so that a lower thrust dynamic pressure bearing portion is definedin the third gap 55. The rotating portion 3 is arranged to rotate whilebeing axially supported by the upper thrust dynamic pressure bearingportion and the lower thrust dynamic pressure bearing portion.

In addition, the inner circumferential surface of the sleeve portion 31is arranged opposite to the outer circumferential surface of the shaft21 with a second gap 54 intervening therebetween. A radial dynamicpressure groove array (not shown) is preferably defined in the innercircumferential surface of the sleeve portion 31 or the outercircumferential surface of the shaft 21 in the second gap 54. The radialdynamic pressure groove array is preferably, for example, a groove arrayarranged in a herringbone pattern. While the motor 12 is running, theradial dynamic pressure groove array induces a dynamic pressure in thelubricating oil 40, so that a radial dynamic pressure bearing portion isdefined in the second gap 54. The rotating portion 3 is arranged torotate while being radially supported by the radial dynamic pressurebearing portion. Note that the number of such radial dynamic pressurebearing portions defined in the second gap 54 may be either one or morethan one.

When the motor 12 is stationary, an upper liquid surface 401 of thelubricating oil 40 is preferably positioned in the upper capillary sealportion 51. In addition, when the motor 12 is stationary, a lower liquidsurface 402 of the lubricating oil 40 is preferably positioned in thelower capillary seal portion 52. As described above, each of the uppercapillary seal portion 51 and the lower capillary seal portion 52 isarranged to decrease in radial width with decreasing height. Each of theupper liquid surface 401 and the lower liquid surface 402 of thelubricating oil 40 thus defines a meniscus by surface tension. As aresult, the likelihood that the lubricating oil 40 will leak through theupper liquid surface 401 or the lower liquid surface 402 issignificantly reduced.

An outer circumferential portion of the first gap 53 preferably includesa portion arranged to increase in axial width with increasing distancefrom the central axis J1. Similarly, an outer circumferential portion ofthe third gap 55 preferably includes a portion arranged to increase inaxial width with increasing distance from the central axis J1. Thus, inthe case where air bubbles are generated in the lubricating oil 40 inthe first gap 53 and the third gap 55, the air bubbles tend to be easilycarried toward the upper capillary seal portion 51 and the lowercapillary seal portion 52, respectively. This contributes to reducingthe likelihood that any air bubble will stay in the first gap 53 or thethird gap 55, and to improving efficiency in discharge of the airbubbles.

An upper labyrinth seal portion 61 is defined by an outercircumferential surface of the circular plate portion 231 and the innercircumferential surface of the projecting portion 342. As mentionedabove, the outer circumferential surface of the circular plate portion231 and the inner circumferential surface of the projecting portion 342are arranged radially opposite each other with the slight gapintervening therebetween. Thus, entrance and exit of a gas through thisgap are limited. This contributes to reducing evaporation of thelubricating oil 40 through the upper liquid surface 401.

A lower labyrinth seal portion 62 is preferably defined by an outercircumferential surface of the outer cylindrical portion 312 of thesleeve portion 31 and the inner circumferential surface of thecylindrical portion 242 of the cup portion 24. The outer cylindricalportion 312 and the cylindrical portion 242 are arranged radiallyopposite each other with a slight gap intervening therebetween. Thus,entrance and exit of a gas through this gap are limited. Thiscontributes to reducing evaporation of the lubricating oil 40 throughthe lower liquid surface 402.

FIG. 4 is a schematic cross-sectional view illustrating the plateportion 23 and its vicinity. The present preferred embodiment will nowbe described below with reference to FIGS. 2 and 4. According to thepresent preferred embodiment, as described above, the coefficient ofthermal expansion of the magnet 33 (not shown) is greater than thecoefficient of thermal expansion of the hub 32. Moreover, thecoefficient of thermal expansion of the cap 34 is greater than both thecoefficients of thermal expansion of the hub 32 and the magnet 33.

The top plate portion 321 preferably includes an increased thicknessportion 3211 and a decreased thickness portion 3212. The increasedthickness portion 3211 is in the shape of a disk, and is arranged toextend radially outward from an outer end of the outer cylindricalportion 312. At least a portion of the increased thickness portion 3211is axially opposed to both the cylindrical portion 242 and the holderportion 222. The decreased thickness portion 3212 is in the shape of adisk, and is arranged to extend radially outward from an outer end ofthe increased thickness portion 3211. The decreased thickness portion3212 of the top plate portion 321 is positioned in a region outside animaginary line “A” extending in the axial direction from an inner end ofeach of the coils 252.

In the case where a heat is applied to the motor 12 from a heat source,such as, for example, a CPU, the hub 32, the magnet 33, the cap 34, andso on expand and are deformed because of the heat. Since the coefficientof thermal expansion of the magnet 33 is greater than the coefficient ofthermal expansion of the hub 32, the degree of axial expansion of themagnet 33 caused by changes in temperature is greater than the degree ofaxial expansion of the hub 32. Thus, a force occurs which pushes anouter end portion 3215 of the top plate portion 321 axially upward withan inner end portion of the decreased thickness portion 3212 of the hub32 as a center. This results in a deterioration in the degree ofhorizontality of an upper surface of the hub 32, with the potentialresult that the motor 12 becomes unable to rotate stably. In addition,the degree or radial expansion of the magnet 33 caused by changes intemperature is greater than the degree or radial expansion of the hub32. Thus, a force which pushes a lower end portion of the tubularportion 322 radially outward with a corner portion 325 of the hub 32 asa center occurs. This force results in a deterioration in the degree ofperpendicularity of an outer circumferential surface of the tubularportion 322. The deterioration in the degree of perpendicularity of theouter circumferential surface of the tubular portion 322 increaseswobbling of each of the disks 11 fixed to the outer circumferentialsurface of the tubular portion 322 when the disks 11 are rotating,leading to a possibility of an error in reading and writing ofinformation from or to the disks 11.

The expansion of the cap 34 can be made greater than the expansion ofeach of the hub 32 and the magnet 33 by selecting the coefficient ofthermal expansion of the cap 34 to be greater than both the coefficientsof thermal expansion of the hub 32 and the magnet 33. Once a sheetdefined by two types of sheets having different coefficients of thermalexpansion joined together is heated and experiences an increase intemperature, the overall sheet bends in a direction toward the sheethaving the smaller coefficient of thermal expansion. This phenomenon iscalled a bimetallic effect. Because of this bimetallic effect, the cap34 reduces a deformation of the hub 32 even in the case where the heatis applied to the motor 12 from the heat source, such as, for example,the CPU, and the hub 32 is deformed. Thus, radial and axial deformationsof the hub 32 are reduced, enabling the motor 12 to rotate stably.

The decreased thickness portion 3212 includes an inner decreasedthickness portion 3213 and the outer decreased thickness portion 3214.An upper surface of the inner decreased thickness portion 3213 is fixedto the lower surface of the plate-shaped portion 341 through theadhesive 90. The outer decreased thickness portion 3214 is arrangedradially outward of the inner decreased thickness portion 3213. Theinner decreased thickness portion 3213 is arranged to have an axialdimension smaller than that of the outer decreased thickness portion3214. According to the present preferred embodiment, the inner decreasedthickness portion 3213 preferably has a radial dimension smaller thanthat of the outer decreased thickness portion 3214. Note, however, thatthe inner decreased thickness portion 3213 may have a radial dimensiongreater than that of the outer decreased thickness portion 3214. In thiscase, an area over which the upper surface of the top plate portion 321is covered with the plate-shaped portion 341 is increased, whichincreases an influence of the bimetallic effect. Accordingly, thedeformations of the hub 32 and the cap 34 are preferably furtherreduced, enabling the motor 12 to rotate stably.

At least a portion of the plate-shaped portion 341 is arranged toaxially overlap with the core back 71. More preferably, at least aportion of the plate-shaped portion 341 of the cap 34 is arranged toaxially overlap with the coils 252. When the hub 32 is deformed becauseof the heat, stress is concentrated on the inner decreased thicknessportion 3213, which has the smallest thickness, and the inner decreasedthickness portion 3213 is deformed to the greatest extent such thathorizontality of the hub 32 is easily affected thereat. When at least aportion of the plate-shaped portion 341 of the cap 34 is arranged toaxially overlap with the coils 252, an area over which the plate-shapedportion 341 of the cap 34 and the top plate portion 321 are adhered toeach other is increased. This contributes to reducing the radialdimension of the decreased thickness portion 3212, where the stressconcentrates most easily, and to further reducing the deformation of thehub 32. In addition, the likelihood that the lubricating oil 40 in theupper capillary seal portion 51 will leak out of the motor 12 through agap between the hub 32 and the cap 34 is reduced.

The lower surface of the plate-shaped portion 341 is fixed to the uppersurface of the top plate portion 321 through the adhesive 90. Since theadhesive 90 is arranged between the lower surface of the plate-shapedportion 341 and the upper surface of the top plate portion 321, the hub32 and the cap 34 are deformed as one single unitary body without beingseparated from each other, even when the hub 32 and the cap 34 aredeformed because of the heat. Accordingly, the bimetallic effect can beobtained such that the radial and axial deformations of the hub 32 canbe reduced. Note, however, that the plate-shaped portion 341 and the topplate portion 321 may not necessarily be fixed to each other through theadhesive 90, but the plate-shaped portion 341 may alternatively be fixedto the top plate portion 321 through press fitting. Also note that bothpress fitting and the adhesive 90 may be used in combination, if sodesired. Also note that the plate-shaped portion 341 may be fixed to thetop plate portion 321 by another method, such as, for example, weldingor crimping.

The inside liquid surface 91 of the adhesive 90 is preferably defined atthe radially inner end of the first adhesion region 901. A secondtapered gap 81 preferably is defined between an upper surface of theincreased thickness portion 3211 and the lower surface of theplate-shaped portion 341. The lower surface of the plate-shaped portion341 preferably includes a cap inclined surface (not shown) arranged toobliquely extend radially inward and axially upward from an inner end ofa region over which the plate-shaped portion 341 and the increasedthickness portion 3211 are in contact with each other. The secondtapered gap 81 is defined by the upper surface of the increasedthickness portion 3211 of the top plate portion 321 and the cap inclinedsurface of the plate-shaped portion 341. The second tapered gap 81 isarranged to decrease in axial width with increasing distance from thecentral axis J1. The inside liquid surface 91 of the adhesive 90 ispreferably positioned in the second tapered gap 81. Note that, accordingto a preferred embodiment of the present invention, the inside liquidsurface 91 is preferably arranged radially outward of the annularportion 311 and radially inward of the stator 25. A strength with whichthe cap 34 and the hub 32 are adhered to each other is preferablyimproved by the inside liquid surface 91 of the adhesive 90 beingdefined between the plate-shaped portion 341 and the outer cylindricalportion 312. The hub 32 and the cap 34 are preferably deformed as onesingle unitary body without being separated from each other when the hub32 and the cap 34 are deformed because of the heat. Accordingly, thebimetallic effect is obtained, and the radial and axial deformations ofthe hub 32 are significantly reduced or prevented.

The second adhesion region 902 includes the outside liquid surface 92 ofthe adhesive 90. An outer circumferential edge of the plate-shapedportion 341 preferably includes an upper inclined surface 341 a arrangedto extend radially outward and downward from a radially outer end of anupper surface of the plate-shaped portion 341. The inner circumferentialsurface of the outer decreased thickness portion 3214 of the decreasedthickness portion 3212, which is radially opposed to an outermostcircumferential surface of the cap 34, includes an upper inclinedsurface 3214 a extending radially outward and upward at least in aregion radially opposed to the upper inclined surface 341 a. A firsttapered gap 70 is defined by the upper inclined surface 341 a and theupper inclined surface 3214 a. The first tapered gap 70 is arranged todecrease in radial width with decreasing height. The outside liquidsurface 92 of the adhesive 90 is preferably positioned in the firsttapered gap 70. The adhesive 90 is held in the first tapered gap 70 bysurface tension. Note that at least one of the upper inclined surface341 a and the upper inclined surface 3214 a may be a curved surface, andthat both the upper inclined surface 341 a and the upper inclinedsurface 3214 a may be curved surfaces. Also note that it is enough thatat least one of the outer circumferential surface of the plate-shapedportion 341 and the inner circumferential surface of the outer decreasedthickness portion 3214 should be inclined with respect to the centralaxis J1. The strength with which the cap 34 and the hub 32 are adheredto each other is improved by the outside liquid surface 92 of theadhesive 90 being defined in the second adhesion region 902. That is,the hub 32 and the cap 34 are deformed as one single unitary bodywithout being separated from each other, even when the hub 32 and thecap 34 are deformed because of the heat. Accordingly, the bimetalliceffect is obtained, and the radial and axial deformations of the hub 32are significantly reduced or prevented.

Referring to FIG. 2, the radial dimension “B” of the first adhesionregion 901 is preferably smaller than a distance “C” from a radiallyouter end of the first adhesion region 902 to a radially outer end ofthe upper surface of the hub 32. As described above, when the disks 11are fixed to the motor 12, the hub 32 and the disks 11 are preferablyfixed by the clamper 15. As a result of the clamper 15 being fixed tothe hub 32 from above, the top plate portion 321 is pressed axiallydownward. This contributes to preventing an axial deformation of theouter end portion 3215 of the top plate portion 321 due to an influenceof the heat. That is, according to the present preferred embodiment, anarea of contact between a lower surface of the clamper 15 and the uppersurface of the top plate portion 321 is increased in order to reduce thedeformation of the hub 32. Further, a sufficient radial dimension of thefirst adhesion region 901 is secured to reduce the deformation of thehub 32 through the bimetallic effect, and to enable the motor 12 torotate stably. Thus, the deformation of the hub 32 is further reduced byarranging the radial dimension “B” of the first adhesion region 901 tobe smaller than the distance “C” from the radially outer end of thefirst adhesion region 901 to the radially outer end of the upper surfaceof the hub 32, and the motor 12 is able to rotate stably.

An uppermost surface of a portion of the plate-shaped portion 341, theportion extending over the first adhesion region 901, is arranged at anaxial level lower than an axial level of an uppermost surface of the topplate portion 321. When the outside liquid surface 92 of the adhesive 90is defined, the adhesive 90 is preferably applied from an axially upperside. At this time, if the adhesive 90 should overflow onto an uppersurface of the outer decreased thickness portion 3214 across the innercircumferential surface of the outer decreased thickness portion 3214,the clamper 15 mentioned above could not be fixed to the upper surfaceof the outer decreased thickness portion 3214 in parallel therewith.Accordingly, the uppermost surface of the portion of the plate-shapedportion 341, the portion extending over the first adhesion region 901,is arranged at an axial level lower than that of the uppermost surfaceof the top plate portion 321, so that the outside liquid surface 92 ofthe adhesive 90 is prevented from being defined above the upper surfaceof the outer decreased thickness portion 3214.

Since the inside liquid surface 91 of the adhesive 90 is positionedbetween the lower surface of the plate-shaped portion 341 and the uppersurface of the increased thickness portion 3211, the lubricating oil 40is preferably prevented from leaking out of the motor 12 through the gapbetween the hub 32 and the cap 34. Further, the outside liquid surface92 prevents the lubricating oil 40 from leaking out of the motor 12through a gap between the plate-shaped portion 341 and the top plateportion 321. Note that another sealant may alternatively be used inplace of the adhesive 90. For example, a resin material other than theadhesive may be used as the sealant.

FIG. 5 is a schematic cross-sectional view illustrating a cap 34A andits vicinity according to an example modification of the above-describedpreferred embodiment. A basic structure of a motor 12A according to thisexample modification is preferably similar to that of the motor 12according to the above-described preferred embodiment.

According to this example modification, a radially outer end portion ofa plate-shaped portion 341A of the cap 34A is preferably arrangedradially outward of radially outer end portions of a plurality of coils252. This results in an increase in an area over which a top plateportion 321 of a hub 32 and the cap 34A are adhered to each other. Thiscontributes to more securely fixing the cap 34A to the hub 32. Inaddition, the likelihood that a lubricating oil 40 in an upper capillaryseal portion 51 will leak out of the motor 12A through a gap between thehub 32 and the cap 34A is significantly reduced.

FIG. 6 is a cross-sectional view illustrating another examplemodification of the above-described preferred embodiment. A basicstructure of a motor 12B according to this example modification ispreferably similar to that of the motor 12 according to theabove-described preferred embodiment.

According to this example modification, a cap 34B preferably includes a“plate-shaped portion projecting portion” 343B arranged to projectdownward from a radially outer edge of a plate-shaped portion 341B. Anouter circumferential surface of the plate-shaped portion projectingportion 343B is fitted and thus fixed to an inner circumferentialsurface of an outer decreased thickness portion 3214 of a top plateportion 321. Inclusion of the plate-shaped portion projecting portion343B in the cap 34B results in an additional increase in an area overwhich a hub 32 and the cap 34B are adhered to each other. Thiscontributes to more securely fixing the cap 34B to the hub 32. Inaddition, the likelihood that a lubricating oil 40 in an upper capillaryseal portion 51 will leak out of the motor 12B through a gap between thehub 32 and the cap 34B is significantly reduced.

While preferred embodiments of the present invention and modificationsthereof have been described above, it will be understood that thepresent invention is not limited to the above-described preferredembodiments.

Note that, only at least one of the upper and lower thrust dynamicpressure bearing portions may be defined without any radial dynamicpressure bearing portion being defined.

Note that spindle motors according to preferred embodiments of thepresent invention and modifications thereof may be either of arotating-shaft type or of a fixed-shaft type. Also note that spindlemotors according to preferred embodiments of the present invention andmodifications thereof may be either of an outer-rotor type or of aninner-rotor type.

Also note that spindle motors according to preferred embodiments of thepresent invention and modifications thereof may be used not only in diskdrive apparatuses but also in a variety of other electronic devices,such as, for example, fans.

Features of the above-described preferred embodiments and themodifications thereof may be combined appropriately as long as noconflict arises.

While preferred embodiments of the present invention and modificationsthereof have been described above, it is to be understood thatvariations and additional modifications will be apparent to thoseskilled in the art without departing from the scope and spirit of thepresent invention. The scope of the present invention, therefore, is tobe determined solely by the following claims.

What is claimed is:
 1. A spindle motor comprising: a stationary portion including a stator; and a rotating portion rotatably supported by the stationary portion through a lubricating oil; wherein the stationary portion includes a shaft arranged along a central axis extending in a vertical direction; the rotating portion includes: a sleeve portion including an inner circumferential surface arranged opposite to an outer circumferential surface of the shaft; a hub made of metal, and including a top plate portion extending radially outward from the sleeve portion, and an outer tubular portion extending downward from an outer edge of the top plate portion; a magnet made of bonded neodymium fixed to the outer tubular portion, and arranged opposite to the stator with a gap intervening therebetween; and a cap made of metal, and including an annular plate-shaped portion fixed to an upper surface of the top plate portion; the magnet has a coefficient of thermal expansion greater than a coefficient of thermal expansion of the hub; and the cap has a coefficient of thermal expansion greater than both the coefficients of thermal expansion of the hub and the magnet.
 2. The spindle motor according to claim 1, wherein a first adhesion region in which an adhesive is located is defined between a lower surface of the plate-shaped portion and the upper surface of the top plate portion.
 3. The spindle motor according to claim 2, wherein the stator includes a plurality of coils; and at least a portion of the plate-shaped portion is arranged to axially overlap with the coils.
 4. The spindle motor according to claim 3, wherein a radially outer end portion of the plate-shaped portion is arranged radially outward of radially outer end portions of the coils.
 5. The spindle motor according to claim 2, wherein an inside liquid surface of the adhesive is defined at a radially inner end of the first adhesion region.
 6. The spindle motor according to claim 2, wherein a radial dimension of the first adhesion region is smaller than a distance from a radially outer end of the first adhesion region to a radially outer end of an upper surface of the hub.
 7. The spindle motor according to claim 2, wherein the top plate portion includes an increased thickness portion at a radially inner portion thereof, and a decreased thickness portion extending radially outward from an outer end of the increased thickness portion; a second adhesion region including an outside liquid surface of the adhesive is defined radially outside the first adhesion region; and an outer circumferential surface of the plate-shaped portion is opposed to an inner circumferential surface of the decreased thickness portion with the second adhesion region intervening therebetween.
 8. The spindle motor according to claim 2, wherein an uppermost surface of a portion of the plate-shaped portion, the portion extending over the first adhesion region, is arranged at an axial level lower than an axial level of an uppermost surface of the top plate portion.
 9. The spindle motor according to claim 1, wherein the cap is made of an austenitic stainless steel.
 10. The spindle motor according to claim 1, wherein the hub is made of a ferritic stainless steel.
 11. The spindle motor according to claim 1, wherein the cap includes a projecting portion arranged to project downward from an inner edge of the plate-shaped portion; and an inner circumferential surface of the projecting portion is arranged radially opposite to an outer circumferential surface of the stationary portion with a gap intervening therebetween.
 12. A disk drive apparatus comprising: the spindle motor of claim 1; a disk supported by the rotating portion of the spindle motor; an access portion configured to perform at least one of reading and writing of information from or to the disk; and a housing configured to accommodate the spindle motor, the disk, and the access portion. 